Certain cellular telephones that exist in the prior art are able to operate on two frequency bands, that is, either around 800 megahertz ("MHz") or around 1900 MHz. (One MHz equals one million cycles per second. 1000 MHz equals one gigahertz.) Established cellular communication networks in the U.S. currently use the 800 to 900 MHz frequency band. The anticipated new PCS ("Personal Communication Services") cellular communication networks in the U.S. will use frequencies in the neighborhood of 1900 MHz. Requirements of these phones, since they are mobile, include that they be small, lightweight, and relatively inexpensive.
In certain prior art systems, dual band operation has required either two band switched local oscillators or three local oscillators in order to perform the up conversion and down conversion associated with superheterodyne operation for both bands. Associated with the multiple oscillator frequencies, multiple filters and mixers complicate the previous dual band designs, causing an increase in the size and cost of these units compared to a single band design.